Referring to FIGS. 1 and 2 the prior art laser indicating pen is illustrated. The pen includes a casing C, a front cover G, a rear cover H, a circuit board I and a mercury battery or a dry battery E. The circuit board I is installed in the casing C. A front end of the circuit board I has a laser diode D resisting against the front cover G and a rear end thereof is connected to a compressible spring resisting against the mercury battery or a dry battery E. An upper end thereof is connected to a key switch A for actuating a switch. A preset circuit is actuated by the casing C so that the DC current in the battery E will conduct the casing C and thus the laser diode D will emit red laser light which is emitted out through a light hole B. When the key switch of the laser diode is pressed, the circuit on the casing C will turn off so that the DC current of the battery E will not conduct with the circuit board D. Thus the laser diode D will not emit red laser light.
From above description, it is known that the power of the laser indicating pen is wholly from the dry battery or mercury battery. Although it consumes less power then a green laser light. However the power of the battery will exhaust (even the laser indicating pen is not used). Thus it is necessary to update a new battery for supplying DC current continuously. The battery can not be used so that it must be deserted. However this will have the problem of environment protection and the cost can not be reduced.